Sourgrass is known to the scientific world as Oxalis pes-caprae.
To gardeners this may be a weed but to hikers and campers.....this is a delicious snack! Although not indigneous to CA, sour grass can be found just about anywhere. A great spot for me to munch is directly in front of my college dorm. I pick up a handful of this stuff to chow down every day! Although the flowers are edible, the most flavorful part of sourgrass is the stem. When you chew on the stem, a sour juice spills into your mouth and gives a sensation much like WarHeads candy. Some people swallow the stem, but the texture freaks me out so i usually just spit it out. There's fields of this stuff everywhere, just look for the super long bright green stems and bright yellow flowers!
Known spot of sourgrass - Sunset Cliffs in front of Point Loma Nazarene University. (San Deigo, CA)